Sight Distance

SSD : is the sum of two distances: perception reaction time, and the vehicle stopping distance.
The curve length should provide enough SSD at design speed, and minimize cut and fill if possible.
AASHTO design standards (1994): H1= 1.07m, drivers eye height, and obstruction height H2 = 0.15m , SSD given in tables.

fig 3.5 , 3-6 mannering